The project includes studies on medical ecology, and the zoogeography, evolution and systematics of fleas, and is primarily based upon collections made during investigations on vectors and reservoirs of rickettsial and viral investigations undertaken in New Guinea, Ethiopia, Burma, Pakistan and other areas. Fleas and other ectoparasites are of interest, concern and importance in medicine for additional reasons than vectorship of major infections. As obligate blood-suckers of warm-blooded vertebrates, with which, in many instances, they have evolved together in intimate association, they serve as aids in our understanding of the relationships, geological history, distribution and ecology of mammals and birds and hence, with the infections harbored or transmitted by such hosts. For example, it was because of the affinities and zoogeography of fleas, chiggers and rodents that had been collected in West Pakistan that members of this Department sought, and found, scrub typhus and tick typhus in totally unexpected geographical regions and habitats in that country. Such observations led to our predictions, since confirmed, that scrub typhus occurs in the USSR; that Soviet viruses were present in Pakistan; and that Central Asian plague exists in the Indian sub-continent. These concepts have led to some generalizations about the ecology of murine typhus and Korean hemorrhagic fever. During the next year, intensive study will be continued on the distribution, host-relationships, phylogeny and systematics of fleas, particularly ceratophyllids, leptopsyllids, pygiopsyllids and hystrichopsyllids. Papers will be prepared primarily on the systematics of the Pygiopsyllidae, the major representative of the Order in the Australian Region, and on some Ethiopian fleas, as well as on Leptopsyllids.